Ethylene slow combustion

Methyl ethyl ketone is unique, in that long and irreproducible induction periods were observed on occasion, reaction ensued only after 7 hours and then was completed within 10 minutes. During the long induction period the only detectable product was methanol. No convincing reason can be advanced to account for this anomalous behavior. The virtual absence of ethylene from the products of the low temperature slow combustion of methyl ethyl ketone strongly suggests that the low-temperature mechanism proceeds almost exclusively by further oxidation of the radicals produced by hydrogen abstraction from the parent ketone. 

In the ease of ethylene, C2H4, it was not to be expected that vinyl alcohol could be detected as a transient intermediate product 4 but force of analogy leads to the assumption that the mechanism of the slow combustion is probably as follows ... 

One somewhat surprising minor product is 1 2-epoxypropane. Its formation parallels the formation of ethylene oxide and 1 1-epoxybutane in the slow combustion of acetone and diethyl ketone, respectively. It may perhaps be formed via... 

In a quartz vessel an equimolar ethylene oxide- oxygen mixture gives rise to cool flames quite readily between about 260 and 380 °C [60]. The slow combustion has been studied in detail above and below the optimum conditions for cool flame formation, and the kinetics in the two regions are quite different [61]. At 420 °C the rate obeyed the law... 

Equilibrium concentrations of carbon or ammonia are not found in short combustion chambers used in rocket motors. The reason for this non-equilibrium situation is that the rate of formation of soot is very slow and carbon does not have time to form. Similarly the dissociation of NH3 is very slow. Thus in ethylene oxide monopropellant rocket motors one finds very little carbon, whereas equilibrium considerations predict carbon as a predominant product and in hydrazine decomposition chambers one finds an excess of NH3 over that predicted by equilibrium considerations. In ethylene oxide motors carbon forms from the decomposition of methane, not the reaction represented above, thus both non-equilibrium situations give higher performance than expected, since the endothermic reactions do not have time to take place. Of course, carbon also could form in cool reactions which take place in boundary layers along the walls where velocities are slow. 

Taylor s experiments180 on the decomposition of metal alkyls led him to believe that the active alkyl groups, released by decomposition of the compounds, functioned in the same way as the active metal atoms. Experiments have shown that the presence of hydrogen atoms induces oxidation of ethylene at room temperature. The theory is advanced that the free alkyl radicals act in a manner similar to hydrogen atoms or metal fogs, i.e., as active oxidation centers producing a slow homogeneous combustion of fuel. This action of free radicals may accomit for the effects of non-metallic knock suppressors as aniline, toluidine, etc. 

---